This invention relates to films for use in the signage industry to increase lighting efficiency.
Lighted signs are everywhere in modern countries. The sign can educate, entertain, inform, or warn the viewer. The sign can be designed for close or distant viewing. Lighting is provided to assure the viewer can see the message, particularly during dimly lit days or nighttime.
Lights require energy to power them. Modern countries readily can provide the power, but those who pay for the energy are always seeking more efficient delivery of the power and more efficient usage of the power. The energy required to power a lighted sign should not be wasted for economic and environmental reasons.
Lighted signs can be xe2x80x9cfront litxe2x80x9d or xe2x80x9cback litxe2x80x9d. The former typically include such signs as billboards or other displays where the light is directed to the sign face from outside of the sign housing and from the same side of the face as the viewer. The latter typically have a translucent surface through which the light is seen and on which the message or image is placed, most often in a sign housing that is internally illuminated. Uniformity of light emanating from the translucent surface is important. Often, the translucent surface includes some element that diffuses the light to reduce the visibility of the point or linear source of the light within the sign cabinet to the viewer. Moreover, typical back lit signage today allows less than 30% of the light emitted from the light source to escape from inside the sign for viewing. Clearly, a more efficient lighting system is needed.
The lighted sign can be in any configuration. Light sources can be of many types, including neon or cold cathode, fluorescent, incandescent, halogen, high intensity discharge (HID), light emitting diodes (LED), and metal halide. The source may be within the housing, or light transported in from an external source by fiber optics or hollow light pipes. The sign can be integral to a building, mounted as a fixture on a building, freestanding, or a part of other apparatus or equipment. The light can be powered continuously, periodically, episodically, or irregularly. Whenever the sign is lighted, the power used should not be wasted.
The lighted sign housing can be any geometric configuration.
Lighted signs that have a perimeter shape of a complex geometry to convey the intended message are entirely different types of signs from lighted signs that rely on the intended message being on a sign face within the perimeter. In the industry, an example of the former type of sign is called xe2x80x9cchannel lettersxe2x80x9d and can generically be called xe2x80x9ccomplex shape lighted signs.xe2x80x9d The latter are called xe2x80x9csign cabinetsxe2x80x9d because the perimeter of the sign is irrelevant to the message being conveyed. Generically, both complex shape lighted signs and sign cabinets can be called xe2x80x9csign housingsxe2x80x9d.
Nonlimiting examples of sign cabinets include rectangular, oval, circular, elliptical, and other geometrical shapes. Nonlimiting examples of complex shape lighted signs include letters, profiles, silhouettes, characters, or any other shape desired by a customer that helps to advertise, educate, warn or the like.
Lighting complex shape lighted signs is more difficult than sign cabinets, because even distribution of the light is quite difficult to obtain unless the light source has substantially the same shape as the viewing area of the sign.
In a back lit sign, the second surface (i.e., inside) of the sign face is sometimes lined with a film (such as 3M Scotchcal(trademark) Blockout Films 3635-20B or 3635-22B commercially available from Minnesota Mining and Manufacturing Company (3M) of St. Paul, Minn.) to block the light from passing through parts of the sign face. This would be done to make a sign where some portion of the sign face would be seen by the viewer as being dark (black) in transmitted light and some other color in reflected light. This is accomplished by lining the backside or the front side of the sign face of a back lit sign with an opaque film. The construction of this film usually has two layers: one black and one white, with the black surface facing into the sign housing and the white surface facing toward the viewer. This construction gives maximum opacity. When a sign is so constructed with the black film or surface facing toward the light source(s) in the sign housing, that portion of the surface area of the inside of a sign housing is black, dark, and light absorbing. The light from the light source hits the front face and where the face is light-transmissive some portion of the light passed through and where the front face is light-blocking, the light is mostly absorbed by the black surface. The percentage of the surface area of the back lit sign that is constructed with a light-blocking, absorbing surface is even greater when the back lit sign has two or more surfaces requiring block out film or the like, such as when a back lit sign is a double message sign or kiosk having more than one surface for sign messages or indicia. Indeed, if the back lit sign has three or more sign faces, then almost all the vertical surfaces of the back lit sign may have light-blocking portions of the sign face constructed partially of light absorbing surfaces.
A similar situation exists when the sign face of a sign is constructed with metal or other material that is cutout, in outline form, to provide the areas where light shall pass through the sign face transmissively.
In either form, blockout film or silhouette, those surfaces facing the inside of the sign housing are not as efficient as they could be in reflecting light back into the sign housing so that such light can eventually emerge from the transmissive portions of the sign face.
The present invention solves the problems in the art by providing a highly reflective film on the inside or outside surfaces of the sign face where light is intended not to be transmitted beyond the sign face.
Preferably, the reflective film is selected from the group consisting of a diffuse reflective film, a semi-specular reflective film, and a specular reflective film having a diffuse reflective film laminated thereto or a diffused coating coated thereto. xe2x80x9cFilmxe2x80x9d means a thin, flexible sheet in existence prior to contact with sign face or sign housing.
xe2x80x9cHighly reflectivexe2x80x9d means a film having at least about 75% reflective as measured using ASTM E 1164-94.
xe2x80x9cDiffuse reflective filmxe2x80x9d means a film that is reflective without being a mirrored surface. xe2x80x9cReflectivexe2x80x9d is an adjective of the noun xe2x80x9cReflectivityxe2x80x9d which is expressed in an industrial standard established by the American Society for the Testing of Materials (ASTM) in Standard ASTM E1164-94, the publication of which is incorporated herein by reference.
A film of the present invention applied to at least some of the light-blocking portion of an interior surface of a back lit sign face surface captures light from the light source or light reflecting back from sides and backs of the light housing and re-directs such light toward the other surfaces of the sign housing for further re-direction eventually through the light-transmissive portions of the sign face and to the viewer. Further, a film of the present invention provides luminance uniformity on the light-transmissive surface of the sign housing.
One aspect of the present invention is a lighted sign housing, comprising a sign face having both light-transmissive portions and light-blocking portions; and a reflective film applied to at least a portion of the light-blocking portions of the sign face. Preferably, the film comprises a diffuse reflective film having a reflectivity of at least 80% as measured using ASTM E1164-94 and, more preferably, selected from the group consisting of polyolefin films filled with white particles, blends of incompatible polymers, polyolefin multilayer films; polyester multilayer films; microvoided polyolefin and polyester films; fluorinated polyolefin films; vinyl chloride polymeric films filled with white particles; acrylic films filled with white particles; polyolefin films co-extruded with ethylene-vinyl acetate films; and combinations thereof.
Another aspect of the present invention is a method of using a film for signage, comprising the steps of selecting a film according to its reflectivity as measured by ASTM E1164-94; and applying the film to at least a portion of light-blocking portions of a sign face of a lighted sign housing.
A feature of the present invention is that the highly reflective film provides a return to the sign housing of light that would otherwise be absorbed or lost from the ultimate brightness of the sign face intended to viewed from the outside of the sign housing.
Another feature of the invention is the reflectivity of the film can be selected to provide desired power consumption reductions and improved luminance uniformity according to the needs of those skilled in the art of signage construction.
An advantage of the present invention is improvement of luminance uniformity while also providing significant power reduction for a sign, such that both utility and aesthetics of a sign are addressed by a single element within the sign housing.
Another advantage of the present invention is that the present invention uses a material that can improve the efficiency of lighted signs and reduce the power consumption required to display a message in a lighted sign as well as improve the luminance uniformity of the sign.
Optionally, but preferably, the reflective film of the present invention is used in conjunction with diffuse reflective films that line at least a portion of the interior walls of the lighted sign housing, as disclosed in copending, coassigned, U.S. patent application Ser. No. 09/070,380 (Deyak et al.) copending, coassigned, U.S. patent application Ser. No. 08/494,366, diffusely reflecting multilayer polarizers and mirrors (such as those disclosed in copending, coassigned, U.S. patent application Ser. No. 08/927,436, microporous membranes (such as thermally induced phase separated films as disclosed in copending, coassigned, U.S. patent application Ser. No. 08/957,558, the disclosures of which are incorporated by reference herein. Use of film of the present invention increases significantly the surface areas within the sign housing that are improved by using a reflective film for increased brightness, decreased power consumption, or a combination of both.
Further features and advantages are disclosed when identifying the embodiments of the invention in relation to the following drawings.